Steam-power plant



Ap 8, 1930. F. l. Du PONT STEAM POWER PLANT Filed April'l. 1921 6 Sheets-Sheet w .m A

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M/VEA/TR Aprll 8, 1930. F. l. Du PoN' STEAM POWER PLANTv Filed April 13. 1921 6 Sheets-Sheet 2 v. /lwf/vrof? Franc/15]. du rz WITNESS.'

F. l. DU PONT April l8, 1930.

STEAM POWER PLANT e sheets-sheet 4 Filed April 15. 11921 F. l. DU PONT' STEAM POWER PLANTl Agra s, 1930.

Filed April 13. 1921v 6 shams-sheet` 6 Ill."

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Patented Apr. 8, v193() l A1,753,335y

UNITED STATES PATENT OFFICE FRANCIS I. nu PONT, or WILMINGTQN, DELAWARE, AssIGNoB. To DELAWAREv CHEMI- CAL ENGINEERING CO., 'WARE 0F WILMINGTON, DELAWARE, A CORPORATION 0F DELA- STEAM-POWER PLANT Application sled 'April 13,

- This invention relates to an improvement 1n steam power plants, and more particularly to a steam power plant for automobiles.

- which can readily be controlled by the driver with very fewcontrol devices.

Another object of theinvention is to provide a system in which the water level in the steam generator or vaporizer is maintained' constant regardless of the steam consumption, by continuously supplying a greater amount of water to the vaporizer than is required for the maximum load and continuously withdrawing the excess Water supplied to the vaporizer and returning it to the Water supply reservoir, and thereby conserve the supply of water; and during the return of the water, extract the heat therein and transfer said heat to the water passing to the Va-` porizer, to prevent the loss ofthe heat contained in the excess water and to raise the temperaturelof the ingoing water.

A further object of my invention is to provide a heating system for the vaporizer adapted for burning kerosene and in which a constant head of oil is maintained as well as a constant air supply; and in which the ingoing air is partially heated by the outgoing waste products of combustion.

A further object of my invention isto conserve the water and heat contained i'n the exhaust steam and return it to the water sup- Aply after assing it 'through a condenser, and cooling t e condenser by passing over the surface thereof the air for the heating system to assist in raising the temperature. of

I the latter.

Another object of my invention is to provide a construction wherein the fuel burner is so located and arranged that it may be observed by the driver without changing his position, and without the opening of a` furnace door, Iwhile the direction of the flow of air to the combustion .chamber is such as to carry the heat of the furnace away from the driver. v l Y Another object of my invention is to prof vide means for feeding the fuel t'o the `combustion chamber and along said chamber by 1921I Serial No. 460,986.

gravity and at the same time provide means for preventing the oil from rapidly flowing to the lowest point on the hearth, so that the oil will be vaporized before it reaches the lowest portion of the furnace.

Another object of my invention is to provide a hearth of fire proof absorbing mate# rial which will absorb the oil to-a certain extent and give it off in the` form of gas, which will prevent the carbonization thereof by the heat in the combustion chamber; and also`to insure a substantially uniform distribution of the evolved gas throughout the entire hearth area.- l p Another object of y invention is to provide a plurality of sets of fuel feeding nozzles and independent control valves therefor, the nozzles of each set bei-11g spaced across the entire front of the combustion chamber so that the oil will be equally distributed over the inlet to the combustion chamber, regardless of whether either or both sets of nozzles are open to the oil sup ly.

Another object of) my invention is to provide means for feeding air to the Vcombustion chamber along the major portion of its length and passing said air over the top or cover of the combustion chamber and through said v will withstand a very high pressure withoutproviding excessively thick walls, as well as a structure in which the sections of tubings can be wc'led to each other at their joints to form a substantially homogeneous, integral and flexible-structure, which will Withstand a hightemperature and pressure without danger of opening up the joints.

Another object of my invention is to so construct the vaporizer as to form a secondary combustionchamber in the lower portion of .the structure 'which will be substantially enclosed by the tubes-of the vaporizer and AWhichwill be in direct communication with lstructures and the duct the outlet endv of the combustion chamber of the oil burner. i

Another object of my invention is to provide a steam superheater or drier in the combustion chamber in the direct path of the hot products of combustion o-insure the de livery of dry steam to the engine. f

Stlll another object of my invention 1s the provision of a long, flexible, composite, tujbular heat'interchanger, adapted to be coiled 1 up in a space above the vaporizer and in the direct path of theA outgoing waste gases, whereby insulation of the interchanger is rendered unnecessary, and whereby the interchanger act to a certain extent as a fuel economizer'by absorbing some of the heat from the waste furnace ases, and transferring said heat to the ingoing feedwater.

A still further and the main object o my invention'Y is the provision of a compact steam plant for automobiles, in which the inherentwaste heat in a system of this type is substantially allreabsorbed and returned to the system through the circulating water system and theair supply, with the exception ofthe heat contained 1n the cooled waste products of combustion and the heat lost by radiation to the surrounding atmosphere ex-v terior vo f the'plant.

The Anature of my invention will he best understood by reference to the accompan ing drawings which will now be describe it being premised, however, that various changes may be made in the details of construction, as well as the arrangement of the parts, without departing from the spirit and scope of my invention as defined in the appended claim.

Fig. 1 of the drawings is alongitudinal sectional view throughl one form of plant built in. accordance with my invention, and in which I show the invention applied to van automobile.

Fig. 2 is a faceview of the burner or furnace and the .oil supply tank, with the burner cover plate removed.

Fig. 3, is a longitudinal' sectional view through a portion of the' burner or furnace, on a larger scale than that shown in Fig. 1.

Figs. 4 and 5, are detail sectional views of the oil feeding devicefor the burner.

Fig. 6, is a transverse sectional view through Fig. 1. Y Y

Fig. 7 is a front view of the air supply duct for the waste products of combustion. Y

Fig. 8, isa'. plan view of the furnace hearth'.

Fig. 9, is aV similar view with the hearth cover in position.

Fig. 10, 1s a transverse sectional view through the'hearth and cover shown in Fig. 9.

` Fig. 11, is alongitudinal sectional view on the line 11-'11 of Fig. 10. Y

12, is a longitudinalfsectional view arge Vscale of a portion of the hearth. v

Fig. 13, is a diagram Ashowing the feed water connections.

Fig. 14, is a plan view of the generator or boiler with the heat interchanger coiled on the top thereof.

Fig. 15, is a detail sectional view through one coil of the interchanger.

Fig. 16, is a diagram illustrating the various steam, water, air, oil and electrical connections.

In these drawings the reference characterl designates the chassis of the automobile, to which is connected thegenerator supporting and casing section 21, and to which are connected theside and end casing plates 22, 23, and 24 are the burner or furnace casing members, which are also supported by the casing section member 21. 25 is an air duct casting connected to the rear end plate 22 of the generator casing and the burner casing member 23. 26 is a sheet metal member .connected at one end to the member and at the other end to the member 24, while the side edges thereof are secured to the side portions of the member 23, to form the air chamber 27 of the burner and a portion of the air duct 28. Supported on the side and end generating casing plates 22 is a sheet metal structure 29, which forms the cover for the generator casing and the outlet duct 30 for the waste products of combustion. Theend lof the conduit 30 is connected to the casing 31, of an exhaust fan, which is su ported on a bracket'32 connected to the en casing plate 22. 33 are outletlducts from the fan casing which extend downwardly and backwardly therefrom. 34 is an electric motor connected to the exhaust fan and an oil pump 35 and is arranged to be driven from a suitable source of energy, as hereinafter descrlbed.

Supported above the sheet metal structure- 29 1s a second sheet metal structure 36, which members 21 and 23.' The hearth extends from the upper end of the burner forwardly and downwardly into what may be termed the secondary combustion chamber within the generator casing. Theprimary combustion chamber' is formed between the face Vof rthe hearth and ajcover plate 38, which separates the main combustion chamber fromthe airchamber 2 7 within the burner.

The hearth 37 is provided with upwardly lng four' oil flow -channels. formed-between.

j extending longitudinal edge ribs 39, and sim- Y larly disposed intermediate ribs 40, there be- .said ribs. The upper face or the hearth is provided with dia-mond'shaped projections 41. The two faces of each projection which extend toward `he inlet end of the burner are substantially normal to the plane of the hearth, while the other faces `thereof are at an angle thereto, to form diagonally disposed intersecting grooves having sloping Walls; the grooves being arranged to cause the oil to flow ina Zigzagmanner downwardly in each channel and across the entire face of the hearth, to evenly distribute the oil and also to prevent the oil from rapidly flowing from the top to the bottom of the hearth.

The longitudinal ribs 40 are not essential where the burner is maintained' stationary, but where the burner is" used in connection with a steam power plant, on a vehicle 0r on a boat, the ribs 40 prevent the oil flowing bodily over to one side in case of rocking of the boat or the travel of a vehicle over a transversely sloping surface.

'I he hearth cover plate 38 is provided with T-shaped air channels in communication with the air chamber 27 which' are arranged alternately with relatively large flame passages above the hearth which form the primary combustion chamber. The bottoms of these air channels are perforated from end to end, but the perforations at the upper end are smaller and somewhat less numerous than at the lower end. lThis is because the rate of vaporization of the liquid fuel is less rapid at the upper end and it is desired to admit air not in proportion to the fuel flowing down the hearth, but Aonly in proportion to that part of the fuel vaporized at any given point. As the fuel travels further down -it encounters zones of greater heat and a large proportion` isv vvaporized and therefore more air is required. Hence the provision of more or less gradual increase in the size and number of the perforations from the upper end to the` lower end. V

Since the volume of flame, that is: of burning vapors, increases as the fuel progresses down the hearth, andV since it is important that this increasing volume shall not interferey with the proper mixing of fresh air with vapor being newly generated on the lower parts of the hearth, flame passages of increasingsize are'provided. The function of these flame passages is to get the burning vapor, which already has its proper amount 'of air,out of the way so as to not obstruct the more delicate process of mixing the new air with new vapor. These flame passages,

Aparticularly at their lower ends, become redhot, and as the air which has to pass into the air channels must pass along and around these flame passages, it becomes highly preheated by absorbing heat therefgro'm; all ofy which makes for efficient combustion.

" A This absorption of heat will be sufficient top revent saidplateibecoming heated to the. point of fusion.

I prefer to form the hearth .of compressed asbestos pulp, so asto form a structure which is fire proof, as well as a structure which will absorb the oil and give it ofi:I in the form of gas. This absorbent` quality, together with the surface formation, will prevent the oil from flowing into the secondary combustion chamber, as the oil will all be absorbed by the hearth before this point is reached. In order to'prevent the oil from passing through the hearth and thence to the secondary combustionchamber between the hearth andthe members 21 and 37, I preferablycoat the bottom face and edges of the hearth with silicate of soda, tov form a coating which is impervious to oil, and thereby prevent any oil passing through the heart The hearth cover plate 38 is preferably formed of nickel or any other metal which will withstand high temperature Without fus.

ing or oxidizing. l

Mounted on the burner casing member 23 1s an oil supply reservoir 42 having a front 'plate 43, and a glass plate therein, through which the driver can see the oil in the reservoir. 44-is an oil feed pipe extending from the pump 35 for delivering oil from an oil supply tank 45 suitably supported from the chassis of the automobile. As the pump 35 is continuously driven by the motor 34 when the burner is in' operation, and is of greater capacwhich front plate i-s provided with a transl parent plate through which the driver can -look into the burner. 48 is a pilot light seated in a recess in the front part of the burner and to which access can be obtained through a small door 49 hinged to the front plate 47; There are provided draft holes 481 of sullicient size to' admit just enough ai-r for the ilot 48.

T e pilot lightlis supplied withfuel from thetank 42 through a pipe 50 having a valve 51v for controlling the feedof oil and a sight tube 52 through which the feed can be observed. Y

The'oil for the burner proper is supplied to the burner by means of a main set .of four jets 53 and a set of four auxiliary jets 54, which are supplied with oil from the -reservoir 42 through the. pipes 55 and 56. respectively.` The pipe 55 is provided with a control valve 5.7 and a pressure controlled valve 58, whlch 1s .connected to the generator or ofgenerating' an excessive pressure in theV steam line therefrom by means of a pipe 58a and is arranged to cut o the supply of fuel i to the main jets when the pressure 1n the generator reaches a predeterminedlimit. The feed pipe 56 is also provided with a valve 59 for controlling the iiow of oil to the auxiliary inclined tapered spout 61, each spout being arrangedlt deliver oil from a pair of jets to the center of a channel on the hearth. AThe pilot light 48, which is placed below the pan is situated centrally between the two intermediate spouts, so that the ame therefrom is drawn onto the hearth between said intermediate spouts by the exhaust fan.

In the drawings I have shown two types of jets, the auxiliary jets 54: merely comprising short tubes opening into a common header and which tubes are directed downwardly toward the pan 60. The auxiliary jets 54 and the control valve 59 in pipe 56 are so proportioned that when valve 59 is fully opened, the quantity of oil delivered to the hearth will only be sufficient to lieep up steam without materially increasing the pressure. ln other words, the heat` generated by oil from the auxiliary jets is merely sucient to compensate for heat lost by radiation, so that the steam pressure can be maintained if desired, when the engine 91 is idle, without danger generator when no steam is drawn from the generator.

The main jets lare of such a size, however, that they will allow to how down the hearth the full amount of oil required for combustion when the burner is working full capacity. As, under these circumstances, the oil feed from these jets is rather heavy and as,

to prevent sediment from clogging the jets,

it is desirable to turn them upward, Iprovide each jet with a cover 530, to prevent the oil from squirting into space.

' The 'main j tending tube and the tubular cover 530 closed at the upper end, the lower end thereof merely resting 'on a coupling between nipples, which couplings and nipples form amanifold for the four jets. As the covers for the Vjets merely rest on the couplings the oil will .ow out around the bottom and into the pan The multiple jet 53 and also the multiple jet 54 are not required where the burner is in a. stationary position. One jet would distrib- Vuta. perfectly well throughout the entire hearth, provided the ribs 40 were eliminated, but on a vehicle or boat, where the burner would be frequently tilted sidewise, maliring ets comprise an upwardly-exit advisable, as hereinbefore explained, to

provide such ribs, the provision of a jet for each channel formed between adjacent ribs is required.

The generator is built up of a plurality of 'l the joints, to form a somewhat exible, homo-V geneous and integral structure.

63 is the upper transverse header and 64 the lower transverse header, to which are connected' the upper and lower longitudinal headers 65 and 66, respectively, of each section. The two outer or side sections are provided with vertical tubesV 67, which extend from header 65 to header 66. Each of the remainder or intermediate sections is provided with only such long tube 67a, which extends from. the upper head 65 tothe lower header 66 at the rear of the boiler'structure and at the front o the automobile, each intermediate section is also provided with intermediate longitudinal header 68, connected at one end to the tube 67a', and the remaining vertical tubes 69 of the intermediate sections are connected to their upper headers 65 and the intermediate headers 68. This forms a secondary combustion chamber open at'the iront end to the burner combustion chamber, and which is bounded on the bottoni by the headers 66, the top by intermediate headers 68, the rear end by the tubes 67, and the sides by the tubes 67. is the generator is formed entirely of short sections of relatively thin gauge, seamless steel tubing, the water in the generator will be rapidly heated and a high pressure can be maintained without danger of an explo- I sion.

rl`he entire interior of the walls of the generator casing are lined with asbestos to retain the heat within the casing and for protecting the walls from the direct action of the flame from the burner.

Mounted on the side of the generator casing Ais a feed water pump 70 of suiiicientcapacity to deliver more than the maximum amount of water required, and a measuring engine or combined pump and engine, 7l for continually removing the excess water delivered to the generator, to maintain a constant level of Water in the generator regardless ofthe steam consumption. Y

. The piston rod of the eed'pump and the water remover are connected to a yoke 72- incassa have used a lurality of such devices, and pre` fer to use t ree pumps vand three water removers set 120 from each other so as to maintain va continuous circulation through the system. A

Coiled on the top of the generator and in the path of the outgoing products of combustion is a heat interchanger 75 which is formed of two tubular members 76 and-7 7 brazed or so otherwise secured to each other as shown in Fig. 15 as to conduct the heat from the one to the other.- The feed water is pumped from the supply tank' 78 by means of the pump 70 through pipe 79, large tube 76 of the interchanger, and pipe 80 to the generator. Leading from the generator to the-measuring engine or excess water remover 71 is a pipe 81, and 82 is a pipe leading from the excess Water remover 71 to the one end of the small tube 77 of the heat' interchangenthe other 'end of said tube 77 being connected to the water supply tank 78. i

1n the normal operation of the device, Water is continually pumped from the sup-I ply tank 7 8 to the generator at a rate in excess of the maximum ldemand for steam for the engine, andthe excess water is continually returned to the supply tank through the interchanger, vso that the level of the water will be maintained on a line with the inlet end of-pipe 81. The capacity of the measuring engine 71 is substantially equal to or greater than that of the pump 70, so that for each complete stroke of these devices a predetermined volume of water will be delivered to the generator, and a predetermined volume l of water or waterland'steam will be removed from the generator and returnedto the tank. The inter-.changer is located in a position in the system where, being immersed in the heated waste gases, it will not need to be insulated, and as the cross-sectional area of the return water tube 77 is relatively small and about feet in length, or of sufficient length to resist the movement of the return fluid, so

that the mechanical energy contained in said fluid by reason of its high pressure will'be converted into heat by overcoming said resist-v ance and the heat will be absorbedby the ingoing water which passes through the interchanger in the reverse direction to the How of excess Huid. The length of the interchanger and diameter ofthe tube 77 are such that suiicient heat is absorbed by the ingoing water, to therebyovercome any danger of the .return water flashing into steam when entering the Water supply tank, and thereby useless'ly losing the heat and mechanical energy in said return water. As the area of the feed Water tube 76 of the interchanger is relatively large the water will not be resisted 1n its movement therethrough and its movement will. also be relatively slow, so that it will absorb substantially'all of the heat from the outgoing water before it enters the generator.

82 isa water gauge mounted on a stationary or fixed portion of the hood and' havin a. .sight glass closed at one end, while the o er end is in communicationwith the generator by means of a pipe 83 The end of this pipe is cut off at an acute angle and is somewhat below the normal water level, but above 4the level to *which the Water can fall without danger. Connected to the upper end of the sight tube is a tube `84`having a valve Which is arranged to 'permit the air to pass frgm the tube and allow the water to fill the tu e. merely pre erential, as, under high steam pressure, thevamount of air that would be forced to the top of the tube would be relatively small. If the water should fall below the end of the pipe 83 steam will enter the pipe and permit -the water therein to pass to the generator. After the water has again risen above the lower end of the pipe it rises l at once filling the sight tube by reason of the steam therein condensing. As the lower end of thepipe 83 is cut at an acute angle there is no danger of thevwater being trapped in the sight tube by means of a globule sealing the lower end of the pipe 83 if the water should fall below the end thereof; l

85 is a steam gauge which is also mounted on a xed portion of the hood, and is c onnected to the generator.

I preferably locate the water and steam gauges at the front of the hood so they will bein the direct line of vision of .the driver.y t

86 and 87 are the upper and lower headers of the condenser which extend along the front and both sides of the automobile in front of the dash and are connected to each other by vertical tubes 88 relatively close to each other to provide the maximum amount of radiating surface, and to cause the air to pass in thin strata to the space under the hood 89. The hood is carried by the condenser so as to be removed with the condenser when the condenser is removed for the inspection of partsenclosed by 'the condenser. V

' 90-is .the live steam'pipe leading from the steam space of the generator to the engine 91, and included in lthe live steam line is a superheater or steam drier 92, which is located in a space in the burner between the maincombustion chamber, andthe secondary combustion chamber, and'93 isa throttle valve in the live steam line between the superheater and the engine. .The exhaust pipe 94 from the engine is connected to'one end of a coil 95 within the supply tank, while the other end to the throttle valve 93, for controlling the admission of steam to the engine 91.

101 lis a source of electrical energy which is connected in series with the motor 34 and a rheostat102, for controllin the speed of the motor, to control the spee of the fan, and

`consequently control the air passing to the burner. Y

In the operation of the plant just described, and assuming that the proper quantity of water is in the generator, valve 5l is first opened lto supply oil to the pilot light 48 which is then ignited, valve 59 or 57 is then opened to supply a quantity of oil to the pan 60 which is allowed to trickle down the channels on the hearth and the circuit is closed through the motor 34 tovcontinuously pump oil to the reservoir 42 and to dravvair through the air conduit 28 to supply air to the combustion, chamber over the hearth. The flame from the pilot light 'will immediately ignite the fuel on the hearth the projections of `which will iunction as Wicks, and after the uel has been ignited the cover plate 38 will soon become heated, which will in turn heat the air so that the burner Will soon generate a high heat. The valve 59 may now be lett wide open as the amount of oil delivered by the auxiliary jets should not be sufficient to raise a high pressure in the generator. The capacity of the jets and the capacity of the fan at the reduced speed having een predetermined relatively to each other, the mixture of uel and air will be such as to vmain-I tain the heat in the generator so that When 'power is not being used a steam pressureV will be maintained.

To get up steam quickly-the valve 57' can be o ened and the rheostat 102 adjusted to give t e fan its full speed, when the main )ets will go into service and steam quickly raised.

The steam when passing through the superheater willbe heated suiiiciently to evaporate all moisture so as to deliver dry steam to the engine.l The exhaust steam will pass `from the engine to the supply tank through the coil 95 in the tank 78 and then through the condenser. '-,The exhaust steam in its passage through the coil 95 will transfer. its heat to the supply water in the tank until this reaches the boiling point and then pass into the condenser in which it will be condensed by contactwith the walls of the tubes 88 which are cooled bythe air passing over the tubes.

The exhaust fan will vcause the air to rush into the air duct and absorb a considerable amount of heat from the outgoing products of combustion through the sheet metal sur.

face 29. The aitlally heated air then passes through t e air chamber 27 into thev combustion chamber, and is heated vto a high temperature in the air chamber as it passes to t e combustion chamber;

The hot products of combustion are sucked into the secondary combustion chamber in the generator and up over the generator tubes as well as the upper and intermediate headers and out through the outlet ducts, and fan chamber. A large portion of the Vheat in .boiler at a rate which is in direct proportion to the speed of 'the engine andthe excess Water is removed vfrom the generator as 'fast as delivered thereto and is returned to the supply tank through the vintercl'ianger in which its heat is transferred to the ingoing Water.

l the pressure in the generator should 'exceed the point at which the pressure control valve, 58 is set, the valve will be closed and shut ed the supply of oil to the main jets 53, and as soon as the pressure in the gener-l ator falls below a predetermined point the valve will again automatically open to feed oil to the main jets As the feed to the pilot light'is alvva s maintained constant, and it desired, the eed to the auxiliary jets there will be'no danger of flooding the burner when the pressure control valve 58 is automatically opened.

H it is desired to leave the automobile confined in a relatively small space, but which is also so arranged that the major ortion of the heat radiated from the system 1s reabsorbed by the in oing air for Vsuporting combustion, while t e excess water Withdrawn from the generator and the Water or condensation together with the heat contained therein are returned to the feed water system,

and thereby conserving both water and heat. A further advantage results from the rovision of means for transferring the eat et stand for a short or long period, the valve from the excess Water to the ingoing Water,

Vwhereby the excess water is resisted in its movement from the generator to the tank so that the mechanical energy contained in said excess water is converted into heat and transferred't'o the ingoing water and which latter' l will cool the excess Water to such an extent before it reaches the su ply tank that thedanger of the Wateras into steam on entering the tank is overcome.

A still further advantage results from the provision of a flexible exchanger adapted to be coiled in a suitable space and formed of a A still further advantage results from the provision of a liquid fuel burner or furnace having a combustion chamber which is downwardly and forwardly inclined from the drivers station, so that the liquid fuel can be delivered by gravity and iow from one end toward the other and at the same time make the front end thereof Containing the pilot o1' vision of a hearth formedv of ireproof ab# sorbing material which will absorb the liquidy fuel and give it oil in the form of gas, and

` which will also prevent the fuel owing to the lowest pointof the' combustion chamber, as the oil will all be absorbed and vaporized be fore this point is reached. The surface of the hearth is also providedwith diagonally disposed intersecting grooves, which are arranged to cause the liquid fuel to' iow 1n a zigzag manner over the surface of the hearth to equally distribute the fuel and also to.

break up the stream; and also from the provision of means for feeding a plurality of spaced liquid fuel streams to the hearth across the width thereof, together with means for preventing the streams from commingling, whereby an even distribution of fuel canbe maintai ned across the full width of the hearth.

Another advantage results from the provision of a liquid fuel burner or furnace hav-` ing an air chamber 'separated from the hearth by'mcans of a covering having perforations .therethrough throughout its length, through which erforations the air passes to the point of com ustion, whereby I am enabled to distribute the air over the entire hearth in such a manner that the air needed for combination with the vaporizing fuel will be supplled approximately in proportion as vapor is generated in each zone of the descending hearth,

tions to form a continuous, homogeneous and flexible structure, which will withstand high temperature, and which will permit of unequal expansion and contraction', as Well as flexing stresses, caused by themovement of the automobile, without opening up at'the v joints. f

The specific features of the burner and water gauge are claimed in United States Letters Patents issued to me on applications filed as of even date herewith No. 1,427,449, dated August 29, '1922, and No. 1,485,492', dated March 4, 1924.

Having now fully described my invention, what I claim and desire to protect by Letters Patent is:

In a power plant, a furnace, a boiler arranged to be heated by the products of combustion from the furnace, a heat interchanger arranged to be heated by the roducts of combustion from the furnace an comprising two tubes, one of which is of relatively small cross-section and the other of whichis of rela-l tively large cross-sectiom'joined together in externalsurface contact with each other, and means for causing liquid to flow from a supply through the larger tube of said heat interchanger into the boiler and for causing fluid to flow from said boiler through the smaller tube of said heat interchanger to the liquid supply, whereby the li uid entering the boiler is heated both by the uid leaving the boiler and by the products of combustion.

InA testimony of which invention, I have 'hereunto set my hand, at Wilmington, Delawam, on this 28th day of March, 1921.

FRANCIS I. DU PONT.

and at the same time highlyheat the air bey fore it is admitted to the combustion chamber. A still further advantage results from the provision of a generator built up from a plurality of sections of steel tubing having relatively thin Wallsand which are welded to each other at the junctions between the sec- 

